Method of and system for telephonic transmission



May 29, 1928. ,671,486

E. s. PURINGTON METHOD OF AND SYSTEM FOR TELEPHONIC TRANSMISSION Filed Dec. 26, 1925 2 sheets-sheet -1 $3 INVENTOR E.s. PuRlNsroN ATTORNEY Patented May 279, 192.8.

UNITED STATES PATENT" OFFICE.

ELLISON S. .P'UlRIIb`(1`rTOI|.\T,l OF GLOUCESTER, MASSACHUSETTS, ASSIGNOR T0 JOHN HAYS HAMMOND, OF GLOUCESTER, MASSACHUSETTS.

METHOD OFQAND SYSTEM FOR TELEPHONIC TRANSMISSION.

Application filed December 26, 192,54. Serial 110.177,777.

This invention relates to aimethod of and` or other telephonie waves is inverted, so that the telephonie waves of lower frequencies are represented by waves of relatively high frequencies, whereas the telephonie waves of higher frequencies are converted into Waves of lower frequencies than the above-mentioned relatively high frequencies, and the` inverted, telephonie waves are caused tol modulate a carrier Wave which is transmitted in sending a message.

A further feature of the invention contemplates inverting the frequency order of the telephonie Waves substantially with-in their own frequency range. One way .in

which this maybe done is by causing them tol modulate current of a frequency near the higher frequency of the telephonie waves'.l

In receiving a message sent in accordance with the invention currents are produced corresponding in'frequencies with the inverted, telephonie waves, and these currents may be caused to modulate current of the same frequency as that modulated by the telephonie Waves at the transmitter, thereby producing energy of the same frequencies and frequency order as the telephonie waves. This energy may then be employed to operate a suitable indicator,

In order to enable the inverted, telephonie Waves to be obtained without intermingling of the original, telephonie waves with them, the inversion of the telephonie waves within a desired frequency range is, preferably, and in accordance with a still further feature of the invention, effected in a plurality of steps so constituted as to enable the inverted, telephonie waves to be readily separated y'by known filtering devices from the original Waves. A preferred method of so performing the inversion of the teleplionic waves is to convert them in inverted frequency order into a higher frequency range and then to step themdown to the desired frequency range without affecting their inverted character. This may be done by causing them to modulate current of a super-audible frequency and by then modulating the lower side band resulting from such modulation by current of a super-audible frequency lower than the firstmentioned, super-audible frequency and differing therefrom by an amount determined by the desired frequency values of the inf' verted, telephonie waves.

The invention also provides a receiver of energy modulated by inverted, telephonie waves including means for producing from the received energy currents having the frequency characteristics of 4the inverted,tlelephonic waves, means for converting said currents into a higher frequency range and simultaneously inverting them to obtain cury rents of tlfe frequency order of the original,

,telephonie waves, and means for stepping down the frequency values of the last-mentioned currents to a desired frequency range which may be that of the original, telephonie waves; These means may comprise modulators which may conveniently be of the vacuum tube typel 'and are preferablyprovided with ,means for supplying them with currents of different, super-audible frequencies respec tively differing from each other by an amount necessary to transpose the inverted, telephonie waves into energy'of the frequencies of the original, telephonie Waves. o

The invention further contemplates the provision of filters wherever required to suppress undersired side bands resulting from modulation or to prevent current supplied to a modulator from intermingling with currents resulting from modulation. p i

Still other objects and features of the invention will be apparent as the description proceeds and will be pointed out in. the appended claims.

In the drawings,l

Fig. 1 is a diagrammatic representation of a transmitting arrangement embodyingthe invention;

' Fig.2 is a diagrammatic representation of a receiving arrangement also embodying the invention; and

Figs. 3 and i show different embodiment-s of the transmitting and receiving arrangements respectively. 4 i

The embodiment of the inventionl illustrated in Fig. 1 of the drawings comprises a A is a vacuum tube modulator 14 of the wellknown push-pull type which suppresses the unmodulated carrier component. The modllator 14 includes two, three-electrode vacuum tubes 16 and 18 and a source 20 of current to be modulated by the telephonie waves produced in the circuit 10.

The modulation of current from the source 20 by the telephonie waves results in the pro` duction of upper and lower side bands, and in order` to suppress one of these side bands, preferably the upper band, a band filter 22 is coupled with the output side of the modulator 14. The filter 22 is also coupled to the input side of a combined modulator and carrier wave generator\24-26 from which eneroy is radiated into the ether by an antenna 28 willich may be tuned to the frequency of the waves produced by the generator 26.

If it,be assumed that the frequencies of the telephonie waves vary within limits of 200 to 3,000 cycles per second, which may be substantially true of speech frequencies, then the frequency of the current produced at the source 20 of the modulator 14 is preferably about 3,000 cycles per second; that is, the frequency of the current at the source 20 preferably lies near the higher frequencies of the telephonie waves.

The modulator 14, in the case assumed, produces an upper side band composed of currents of frequencies: between 3,200 and 6,000 cycles per second in which the frequency order of the telephonie waves is not inverted and a lower side band composed of currents of frequencies between zero and 2,800 c cles per second respectivel in which t e frequency order of the telepiionic WavesV is inverted. The filter 22 suppresses currents belonging to the upper side band and impresses upon the modulator-generator 24-26 inverted, telephonie waves Varying in fre uency between zero and 2,800 cycles. It wil appear clearly from the foregoing that the frequency values of the inverted, telephonie waves depend upon the frequency of the current supplied from the source 20.

For example, if the frequency of the cur-v lrent at the source 20 was 4,000 cycles per second instead of 3,000, the frequency values of the inverted, telephonie waves would lie within limits of 1,000 cycles and 3,800 cycles respectively. It will further be understood that the provision of current of a frequency of 3,000 cycles per second at the source l2O of the modulator 14 causes the inverted, telephonic wavesV to lie Within substantially the same frequency range as do the original, telephonie waves, or, in other words, the range of frequency values ofthe inverted, telephonie waves is to a considerable degree the same as that of the original, telephonie. Waves.

The arrangement shown in Fig.l 2 for receiving energy, modulated by the inverted,

telephonie waves and radiated by the antenna 28, comprises an antenna 30 connected with the input side of a vacuum tube detector 32. The output side of the detector 32 is coupled with a similar to the modu ator 14 of Fig. 1 and including two, three-electrode vacuum tubes 36 and 38 and asource 40 of current of the same frequency vas that of the source 2-0 of the modulator 14, namely, in the case assumed, 3,000 cycles. The output side of the modulator 34 is coupled with a band filter 42 connected with a suitable indicator 44 which may, as shown, be in the form of a telephone receiver.

The detector 32 produces from the energy induced in the antenna 30 currents of frequencies corresponding with the frequencies of the inverted, telephonie waves impressed upon the modulator-generator 24-26 of Flg. 1. The frequencies of such currents, in

the case assumed, would lie within limits of ush-pull modulator 34' zero and 2,800 cycles per second respectively.

These currents in the device 34 modulate current of a frequency of 3,000 cycles per second provided from the source 40, thereby.

reducing upper and lower side bands, the atter of which varies in frequency between limits of 200 and 3,000 cycles per second in the same manner as do the original, telephonie waves. The currents in the lower side band are, moreover, of the same frequency order as the original, telephonie waves. The filter 42 suppresses the upper side band resulting from the action of the modulator 34 and' passes the lower side band of frequencies from 200 cycles to 3,000 cycles so that they may operate the telephone receiver 44.

The inversion of the telephonie waves before they are impressed upon the modulatorgenerator 24-26 of Fig. 1 renders the message unintelligible to one employing an ordinary type of receiver. However, a messagetransmitted from an arrangement such as is shown in Fig. 1 may-not only be received by the arrangement shown in Fig. 2,

but may be of as good,quality as though no effort had been made to send it secretly.

If itis not desired that the telephonie message received at the indicator 44 shall be. of exactly lthe same pitch as that impressed upon the transmitter 12 of Fig. 1, the current at the source 40 of the modulator 34 may not be of precisely the same frequency as that at the source 20 of the modulator 14. A difference in frequency of the currents at these' sources will change the pitch of the message to a corresponding degrec. but if the difference is nottoo great, will 4nel: preventy the message from being inteiligibly received.

In the modified form of transmitter shown in Fig. 3, the circuit 50 including the telephone transmitter, the bandiilter 52 Y 3, however, the inversion of the telephonieV waves is accomplished in two steps so constituted as to enable the inverted, telephonie waves to be readily obtained free from undesired currents. As shown, the means for inverting the telephonie waves includes a modulator '60 comprising two, three-elec trode vacuum tubes 62 and 64. The modulator 60 is similar to the modulator 14 of Fig. 1 except that it is provided with a source 66 of current of different frequency. The frequency ofthe current at the source 66 may, for example, be 33,000 cycles per second. l

` The modulator 60 is connectedwith a,.til ter 68 also connected with a second modulator 70 which may as shown comprise-'a single three-electrode vacuum tube and a source 72 of current of a frequency differing from the frequency of the current at the source 66 by anv amount depending upon the desired value of the frequency range of the inverted, telephonie waves. The modulator 70 comprises windings 74 and 76 in its grid-filament circuit coupled respectively with the filter 68 and the source of current 72.

In the operation of the transmitting arrangement shown in Fig. 3, the telephonie waves produced in the circuit 50 are caused to modulate current of the frequency of the source 66, for example, 33,000 cycles per second. The modulator 60 produces upper and lower side bands of such frequency and itself suppresses the unmodulated current of 33,000 cycles. The band filter 68 suppresses the upperside band and passes the lower side band, the frequencies of which,in ,the case assumed, vary between 30,000 cycles and 32,800 cycles per second. Currents of the last-mentioned frequencies are then impressed upon the modulator 70 along with currents supplied at the source 72 of a frequency, for example, of 30,000 cycles per second. Since the modulator 70, as shown, is not of the type which suppresses the unmodulated carrier component, the output circuit of the modulator 70 will contain c urrents of a frequency of 30,000 cyclesper second, currents of frequencies of 30,000 toV 32,800 cycles per second, and upper and lower side bands of such frequencies.

From the foregoing, it will be understood that the modulator 60 acts to invert and step up the frequencies of the telephonic waves, the band filter 68 passes the inverted and stepped up waves and suppresses the noninverted waves of the upper side band, the

the inverted, telephonie waves without af- `ecting their inverted character and the band filter 53 suppresses all-currents other than the desired, inverted, telephonie waves.

The use of current of al super-audible fre quency, such as 33,000 cycles per second, at the modulator 60 causes the inverted Waves passed by the band filter 68 to lie within a range of frequencies remote from that of the telephonie waves so that the desired, inverted waves can be readily separated from the vtelephonic waves by known filters. Moreover, currentof the carrier frequency is suppressed due to the construction ofl the modulator 60 and does not pass to the filter 68. Accordingly, such filter impresses upon the modulator 70 the inverted, stepped-up, telcphonic waves unmixed with any undesired currents. TheV currents supplied to the modulator 70 are allof frequencies so far different from the frequencies of the lower .side band which the band filter 52 is de-v impressed upon the modulator-generator 54--56 are caused to be of the same range of frequencies as those obtained by inversion of the telephonie waves in Fig. 1, namely, in the case assumed, zero to 2,800 cycles per second. The reason for this is that the frequencies 133,000 and 30,000 cycles differ by an amount equal to the frequency of the current provided at the source 20 of Fig. 1, namely, 3,000 cycles." That the frequency range of the inverted, telephonie waves supplied by the band filter 52 in Fig. 3 is gov-I crned by the difference in frequencies of the currents at the sources 66 and 72 can readily be seen,.if it is assumed that the frequency of the current-at the source 66 remains at 33,000 cycles and current of the frequency of 29,000 cycles per second is provided at the source 72 in which case the inverted, telephonie waves in the lower .side band produced by the modulator 70 will range in frequency between 1,000 cycles and- 3,800 cycles per second, and if it is .then assumed that the frequency of the current at the source 66 is 32,000 cycles, whereas current of 29,000 cycles is provided at the source 72, in which case they frequency range of the lower side band produced by the modulator 70 will again be between zero and 2,800 cycles;

The receiving arrangement shown in Fig. 4 of the drawings is designed to receive energy modulated by inverted, telephonie.

waves with the same freedom from intermingling of undesired currents with currents of desired frequencies as is lobtained in the transmitting arrangement of Fig. 3. The receiving arrangement illustrated in Fig. l comprises an antenna 80 connected with the input side of a detector 82, the output side of which is connected with a modulator 84 including two, three-electrode vacuum tubes 86 and 88 and a source 90' of current of super-audible frequency, for example, 33,000 cycles per second. The modulator 84 is connected with a band filter 92 the'output side of which 'is in turn coupled with a modulator 93. The input side of .the modulator 93 comprises windings 94' and 96 coupled respectively with the band filter 92 and a source 98 of current ofsuper-audible frequency. for example, 33,000 cycles per second. Connected with the output side of the modulator 93 is a band filter -100 which passes current to the circuit of, a. telephone receiver 102.

The detector 82 produces from the energy induced in the antenna current of fre--l quencies corresponding with those of the inverted, rvtelephonie waves employed to modulate the transmitted carrier Wave.v These currents in the case assumed vary through -a frequency range of zero to 2,800 cycles per second and are caused to modulate current of 33,000 cycles provided from the source 90. The modulator 84 itself suppresses unmodulated currentof the fre' quency of 33,000 cycles, and the upper side band produced by the modulator isy suppressed by the filter 92 which impresses upon the modulator 93 currents belonging to the lower side band produced by the modulator 84 and varying in frequencies from 30,20() cycles to 33,000 cycles per second. T he modulator 93produces from the lower side band 4of the modulator 84 currents ranging'in frequencies from 200 cycles to 3,000 cycles per second. It'will be noted that these currents are of the same frequencies as those set up in the telephone translnitter circuit 50 of Fig. 3 and are,

moreover, of the same frequency order as the telephonie Waves produced in the circuit 50. Accordingly, the currents will reproduce at the receiver 102 the message impressed upon the transmitter arrangement.

The frequency of the current provided at the source 98 of the modulator 93 is in the case assumed of a value less than the frequency-33,000 cycles-of the current produced at the source by an amount such as to reproduce telephonie waves of an original frequency range from 200 tov 3,000 cycles =from inverted, telephonie Waves ranging In frequency from zero to 2,800 cycles. If telephonie Waves ranging in frequency from 200 `to 3,000 cycles per second were inverted in a frequencyv range different from zero to 2,800 cycles, the difference between the frequencies 'of the currents provided at the sources 90 and 98 respectively of the receiving arrangement of Fig. 4 must be correspondingly modified if it is desired to reproduce the telephonie Waves in their original frequency range.E Moreover, by suitably selecting the frequencies of the currents of the sources 90 and 98, the telephonicwaves may,.if desired, be reproduced in their original frequency order but at different frequency values or pitch, as will be clear from the discussion given above of the receiving system shown in Fig. "2.,

When the system shown in Fig. 4 is employed to receive-from a transmitting arrangement such as is shown in Fig. 3, the difference in frequencies of the currents at the sources 90 4and 98 must be the saine as the diiference in frequencies of thecurrents at the sources 66 and 72 of Fig. 3 in order to reproduce the message at the same frequencies as those ofv the telephonie waves set'up in the telephone transmitter circuit 50 of Fig. 3.

The receiving arrangement shown in Fig. 4 is not, however, restricted to use with the transmitting system shown in Fig. 3, but may also be utilized in receiving messages from a transmitting arrangement of the kind shown .in Fig. 1.

Detailed description of t-he modulators 14, 34, 60 and 84, the modulator-generators 24-26 and 541-56 and of the band filters shown herein is deemed unnecessary because all of these devices may be and as shown are of Well-known construction and constitute per se no part of the present invention.

While the invention has been described as applied to a radio transmitting and receiving system; it isto be understood that the invention is equally applicable to other Atypes of transmission, such as transmission llU Verted character, and transmitting a carrier I wave modulated by the inverted, telephonie waves.

2. A. method of secret, telephonie transmission which includes producing telephonie waves, inverting the frequency order of saidwaves by successive modulations of currents of frequencies dlferent from each other and from the last modulation which does not fnmission Which includes producing telephonie Waves, inverting the frequency order of said waves by causing themto modulate current of a lngher frequency ,than the telephonie waves, suppressing the upper side .band resulting Cfrom said modulation, modulating the lower side band by current of a frel' quency diiierent from the above-mentioned,

modulated frequency and also outside of the frequency range of the telephonic waves and suppressing tie upper side band resulting from the last-mentioned modulation, modulating a high frequency carrier Wave by the inverted, telephonie waves and transmitting the carrier wave.

4. A method of secret, telephonie transmission which includes producing telephonie waves, -inverting the frequency order of said waves by causing them to modulate current of a superaudible frequency and causing the lower side band resulting from said modulation to modulate current of a` second- `superaudible frequency lower than the an amount determined by the desired value of the frequency rangel of the inverted, telephonie- Waves, modulating a carrier Wave 'by the inverted waves and transmitting the carrier wave.

5. A method of secret, telephonictransmission which includes producing telephonie waves, inverting thefrequency order of said Waves within a. desired frequency range by converting them in inverted frequency order into a high frequency range and then stepping them down to the desired frequency range without affecting their inverted character, transi'nitting a carrier wave` modulated by the inverted, telephonie Waves,lpro ducing from thel carrier Wave currents having the frequency characteristics of the inverted, telephonie waves, converting 'said currents into a higher frequency range and simultaneously inverting them to obtain currents of the frequency order of the original, telephonie waves, stepping down the frequency values of. the last-mentioned cur-- rents substantially to those of the original,

I telephonie waves, and causing the resultant currents to operate an indicator.

6. A methodof secret, telephonie transmission which includes producing telephonie waves, inverting the frequency order of said waves by successive modulations of currents -of frequencies different from each other and higher than the frequencies of the telephonie4 waves, suppressing the side band resulting from the last modulation which does not include waves corresponding to the telephonic waves in inverted frequency order, modulating a carrier Wave by the inverted telephonie waves, transmitting the carrier Wave, producing from Lthe carrier wave energy havingthe frequency characteristics of the inverted telephonie waves, successively modulating by said last-mentioned energy higher frequency currents ydiffering in frequency by substantially the same amount as the difference between the frequencies of the first-mentioned currents to produce energy having the frequency characteristics of the telephonie waves, and causing said last-mentioned energy to operate an indicator.

7. A method of secret, telephonie transmission Which includes producing telephonie Waves, inverting the frequency order of said waves by causing them to modulate current of a. higher frequency than the telephonie waves, suppressing the upper side band resulting from said modulation, modulating the lower side band' by current of a frequency different from the above-mentioned, modulated frequency and also higher than the frequencies of the telephonie Waves and suppressing the upper side band resulting from the last-mentioned modulation, modulating a high frequency carrier wave by the.

inverted, telephonie waves, transmitting the carrier wave, producing currents having the frequency characteristics of the inverted, telephonie waves, modulating by said energy current of the same frequency as the firstmentioned current, suppressing the upper side band resulting from said modulation, modulating' the lower side band resultlng therefrom by current of the same frequency as the second-mentioned current to produce energy having the frequency characteristrcs of the telephonie waves, and causing said last-mentioned energy to operate an indicator.

8. A method of receiving energyl modulated by inverted, telephonie waves which consists in producing from the received energy currents having the frequency characteristics of the inverted, telephonie waves, convert- 'ing said currents into a higher frequency transmitting the Vcarrier waves.

11. A secret, telephonie transmission system, including means for producing telephonic Waves, a modulator for invertlng the requency order of the telephonie waves and stepping them up to a higher range of frequencies, a second modulator for stepping down the inverted Waves to substantially the frequency levelI of the telephonie waves, means for producing a carrier wave, means for modulating the carrier wave by the inverted telephonic waves andv means for transmitting the carrier waves.

152,.y A secret, telephonie transmission systerm' including means for producing telephonie waves, a modulator for inverting the frequency order of the telephonie waves and stepping them up to a higher range of frequencies, asecond modulator for stepping down the inverted Waves to substantially the frequency level of the telephonie waves, means for producing a carrier wave, means for modulating the carrier wave by the'inverted telephonie waves, means for transmitting the carrier waves, means including a vacuum tube detector for producing from the carrier Wave energy of the frequencies of the inverted, telephonie waves, means for modulating by said last-mentioned energy current of the same frequency as the modulated current in the first-mentioned modulator, means for modulating a side band resulting from the last-mentioned modulation by current of`a frequency employed in the second-mentioned modulator, and an indicator operated by currentsresulting from the last-mentioned modulation.

13. A receiver for energy modulated by inverted, telephonie waves comprisin means for producing from the transmitte ener currents having the frequency character1stics of the inverted, telephonie waves, means for converting said currents into a higher frequency range and simultaneously inverting them to obtain currents of the frequency order of the original, telephonie waves', means for stepping down the frequency values of the last-mentioned currents substantially to those ofthe original, telephonic waves and an indicator operable by the resultant currents. 14. A- receiver for energy modulated by 1nverted,telephonic waves, including means for producing currents of frequencies equal and correspondingnto those ofthe inverted, telephonie waves, means for modulating by said last-mentioned currents current of a substantially higher frequency than the telephonic Waves, means for modulating currents resulting from the first-mentioned modulation by current of a frequency differing from that of the first-mentioned, modulated current by an amount such as to produce currents having frequencies sub stantially equal to those of the original, telephonic waves, and al1 indicator connected With the last-mentioned modulating means. 15. A receiver for energy modulated by inverted, telephonie waves including means for producing currents of frequencies corresponding to those of the inverted, telephonie waves, said means including a detector, means for modulating by said lastmentioned currents current of a super-audible frequency, means for modulating currents resulting from the first-mentioned modulation by current of a lower, super-audible frequency differing froni the quency of the first-mentioned, modulated current by an amount such as to produce currents having frequencies equal to 'those of the original, telephonie waves, and an infredicator connected with last-mentioned modv ulating means.

16. A receiver for energy modulated by inverted telephonie waves including means for producing currents of frequencies corresponding to those of the inverted, telephonic waves, said means including a detector, two modulators connected with the output side of the detector in cascade relation with each other, means for su plying said modulators with currents of iierent, super-audible frequencies respectively, and an indicator connected with the second modulator.

ELLIsoN s. PURINGTON. 

